To define hormonal factors responsible for gastric hypersecretion in duodenal ulcer disease in man. To test the hypothesis that circulating concentrations of gastrin, one of the different molecular types of gastrin, or another acid-stimulating hormone are increased inappropriately in such patients due either to increased rates of release or decreased rates of metabolism. Metabolism will be studied by infusion of purified natural forms of human gastrin in man. Tissue distribution and release of gastrin will be measured by radioimmunoassay. Other hormonal stimulants will be detected by bioassay of plasma extracts in dogs with gastric pouches. The aim of these studies is to gain insight into the pathogenesis of peptic ulcer disease in man.